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排序方式: 共有168条查询结果,搜索用时 15 毫秒
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M. Bonesini E. Bonvin P. S. L. Booth L. J. Carroll A. J. Cass D. Cavalli G. Cecchet G. Costa M. Donnat P. A. Dorsaz D. N. Edwards J. R. Fischer L. Fluri D. Frame F. Gianotti S. Jack J. N. Jackson M. Kelly M. N. Kienzle-Focacci R. Lucock J. G. Lynch L. Mandelli M. Martin L. Mathys A. Maxwell M. Mazzanti J. J. Myerscough P. J. Negus S. Pensotti-Rancoita L. Perini D. Perrin G. Polesello W. H. Range L. Rosselet S. W. Snow A. S. Thompson R. M. Turnbull J. Wells M. Werlen WA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,38(3):371-382
The inclusive cross sections for production of prompt photons and π0 s by 280 GeV/c protons incident on a liquid hydrogen target, have been measured forp T in the range 4.0 to 6.5 GeV/c and for |x F |<0.45. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed. Phenomenological fits to the π0 and prompt photon cross sections are given. 相似文献
64.
A three component catalyst system entailing an amino acid (O(t)Bu-L-threonine), a hydrogen bond donor (sulfamide), and an amine base (DMAP) allows α-branched aldehyde addition to nitroalkenes in good to high yield and excellent ee. Importantly, the lowest reported catalyst loading (5.0 mol%) and aldehyde stoichiometry (1.2-2.0 equiv) is demonstrated and in most instances the best current product profile is observed. 相似文献
65.
Prof. Dr. Thomas C. Nugent Abdul Sadiq Ahtaram Bibi Prof. Dr. Thomas Heine Lei Liu Zeonjuk Dr. Nina Vankova Dr. Bassem S. Bassil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):4088-4098
Relying on the assembly of commercially available catalyst building blocks, highly stereocontrolled quaternary carbon (all carbon substituted) formation has been achieved with unmatched substrate diversity. For example, the in situ assembly of a tricomponent catalyst system allows α‐branched aldehyde addition to nitroalkene or maleimide electrophiles (Michael products), while addition to an α‐iminoester affords Mannich reaction products. Very good yields are observed and for fifteen of the eighteen examples 96–99 % ee is observed. Using racemic α‐branched aldehydes, two contiguous (quaternary–tertiary) stereogenic centers can be formed in high diastereo‐ and enantiomeric excess (eight examples) via an efficient in situ dynamic kinetic resolution, solving a known shortcoming for maleimide electrophiles in particular. The method is of practical value, requiring only 1.2 equiv of the aldehyde, a 5.0 mol % loading of each catalyst component, for example, O‐tBu‐L ‐threonine (O‐tBu‐L ‐Thr), sulfamide, DMAP or O‐tBu‐L ‐Thr, KOH, and room temperature reactions. As a highlight, the first demonstration of ethylisovaleraldehyde ( 7 ) addition is disclosed, providing the most congested quaternary stereogenic carbon containing succinimide product ( 8 ) known to date. Finally, mechanistic insight, via DFT calculations, support a noncovalent assembly of the catalyst components into a bifunctional catalyst, correctly predict two levels of product stereoselectivity, and suggest the origin of the tricomponent catalyst system’s exceptionality: an alternative hydrogen bond motif for the donor‐acceptor pair than currently suggested for non‐assembled catalysts. 相似文献
66.
Keith A. Nugent 《Contemporary Physics》2013,54(1):55-69
The concept of phase is deeply instilled in the mind of every physics student from a very early age and its measurement seems inevitably intertwined with the need to perform interferometry. More recently, a number of important phase visualisation and measurement techniques have emerged that do not require interference. This paper introduces the concept of phase by treating it as a potential that determines the flow of energy, which leads to the idea that phase can be measured by observing the evolution of the intensity of the light on propagation. The ideas have found application in a number of areas, including optical, X-ray, neutron and electron imaging physics and these are explained. 相似文献
67.
We prove that in the absence of phase singularities, a generalized Schell model partially coherent field is fully defined by its intensity in three planes. We discuss the implications of this result for the problem of characterizing wave fields. 相似文献
68.
Lenneke WA van Hooijdonk Muhammad Ichwan Thomas F Dijkmans Theo G Schouten Marijke WA de Backer Roger AH Adan Fons J Verbeek Erno Vreugdenhil Carlos P Fitzsimons 《BMC neuroscience》2009,10(1):2-19
Background
In the adult hippocampus, the granule cell layer of the dentate gyrus is a heterogeneous structure formed by neurons of different ages, morphologies and electrophysiological properties. Retroviral vectors have been extensively used to transduce cells of the granule cell layer and study their inherent properties in an intact brain environment. In addition, lentivirus-based vectors have been used to deliver transgenes to replicative and non-replicative cells as well, such as post mitotic neurons of the CNS. However, only few studies have been dedicated to address the applicability of these widespread used vectors to hippocampal cells in vivo. Therefore, the aim of this study was to extensively characterize the cell types that are effectively transduced in vivo by VSVg-pseudotyped lentivirus-based vectors in the hippocampus dentate gyrus. 相似文献69.
Prof. Thomas C. Nugent Foad Tehrani Najafian Hussein Ali El Damrany Hussein Ishtiaq Hussain 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14342-14348
Site selectivity, differentiating instances of the same functional group type on one substrate, represents a forward‐looking theme within chemistry: reduced dependence on protection/deprotection protocols for increased overall yield and step‐efficiency. Despite these potential benefits and the expanded tactical advantages afforded to synthetic design, site selectivity remains elusive and especially so for ketone‐based substrates. Herein, site‐selective intermolecular mono‐aldolization has been demonstrated for an array of prochiral 4‐keto‐substituted cyclohexanones with concomitant regio‐, diastereo‐, and enantiocontrol. Importantly, the aldol products allow rapid access to molecularly complex ketolactones or keto‐1,3‐diols, respectively containing three and four stereogenic centers. The reaction conditions are of immediate practical value and general enough to be applicable to other reaction types. These findings are applied in the first enantioselective, formal, synthesis of a leading Alzheimer's research drug, a γ‐secretase modulator (GSM), in the highest known yield. 相似文献
70.
David G. Ahern Judith A. Egan Richard P. Nugent Crist N. Filer 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):1029-1031
The high specific activity tritiation of oxymorphone and pentamorphone is described. 相似文献